Today's catch on CPAN: Time::Duration
I needed to print out human-friendly "seconds left until completion" (i.e. "1 hour and 5 minutes") and figured someone else had done that already.
It took me no more than two minutes to find, install and use the module.
CPAN remains _the_ best example of software reuse that I've ever encountered, all categories (and that's considering that my final paper at university was titled "Organizational aspects of software reuse").